As is commonly known, an optical storage disc comprises at least one track, either in the form of a continuous spiral or in the form of multiple concentric circles, of storage space where information may be stored in the form of a data pattern. Optical discs may be read-only type, where information is recorded during manufacturing, which information can only be read by a user. The optical storage disc may also be a writable type, where information may be stored by a user. For reading/writing information from/into the storage space of the optical storage disc, an optical disc drive comprises, on the one hand, rotating means for receiving and rotating an optical disc, and on the other hand optical means for generating an optical beam, typically a laser beam, and for scanning the storage track with said laser beam. Since the technology of optical discs in general, the way in which information can be stored in an optical disc, and the way in which optical data can be read from an optical disc, is commonly known, it is not necessary here to describe this technology in more detail.
In a disc drive, several operational parameters need to be calibrated, i.e. set to an optimal value for optimal performance. For example, a tilt angle of an optical lens is calibrated, a focus offset of an optical pickup unit is calibrated, a radial error amplitude is calibrated, etc. Particularly, in the case of a write operation, the optical write power is calibrated. Said parameters are commonly known to persons skilled in this art, as is the requirement for calibration. Further, calibration procedures for the above-mentioned and other parameters are known per se, and may be used in implementing the present invention. Therefore, a more detailed description of calibration procedures is not necessary here.
It is already known in practice to perform calibration procedures as part of a start-up procedure or initiation procedure, i.e. when a new disc is introduced in the disc drive, and/or when a new read/write command is given in respect of a disc already present in the drive. However, it may be that the parameter values as set during start-up calibration are no longer optimal values at a later stage of the read/write process. This may, for instance, be due to changing circumstances like changing temperature, changing read/write location on disc, etc. Therefore, it may be desirable to also perform calibration procedures at a later stage, when a write or read process is in progress. Such calibration procedures will be indicated by the phrase “recalibration”, to make a distinction from calibration during the start-up phase.
An important aspect in recalibration is its timing. On the one hand, more frequent recalibration procedures may improve the signal quality, but it involves a reduction in data throughput. On the other hand, if recalibration procedures are performed not often enough, errors may occur. Further, recalibration procedures interrupt the write or read process which is in progress, so they could affect the proper data transfer.